Liquid polymeric dimethyl silicones



Patented Oct. 26, 1948 LIQUID POLYMERIC DIME'I'HYL SILICONES Rob RoyMcGregor, Verona, and Earl Leathen Warrick, Pittsburgh, Pa., assignorsto Corning Glass Works, Corning, N. Y., a corporation of v New York 7 NoDrawing. Application April 2, 19 45,

- Serial No. 586,270

I 11 Claims, (CL 260-4483) This invention relates to the preparation anduse of liquids having lubricating properties and specificallycharacterized by high resistance to oxidation, little change ofviscosity with temperature and low pour point, as determined by the A.S. T. M. standard method for lubricants.

This application is a continuation-in-part of our copendingapplications, Serial Number 432,530, tiled February 26, 1942 (now PatentNo. 2,384,384, patented September 4, 1945), and Serial Number 481,143,filed March 30, 1943 (now Patent No. 2,437,204, patented March 2, 1948),both of said applications being assigned to the assignee of the presentinvention.

The lubricants in common use are for the most part petroleum oils. Whilethey have a wide range of use they have certain inherent defects whichmake them inapplicable or only poorly applicable under certainconditions. The most evident of these defects are their ease ofoxidationor inflammability. instability at high'temperature as evidenced by acidformation and viscosity increase-inability to lubricate at lowtemperatures, and their great change of viscosity with change oftemperature. Liquids which do not have these defects would be useful infields where abnormal or subnormal temperatures are to be encountered orwhere high concentration of oxygen makes the use of petroleum oilshazardous.

. and the provision of such liquid is the primary object of thisinvention. 7

Other objects will be perceived in the following description of our newliquids, their constitution, properties and uses and the methods bywhich they may be produced, all of which contribute to the variousembodiments of our invention.

, 2 organic radical is attached to the silicon atom and which are highlypolymeric and are repre- 1 sented by the unit structure i-O- i As afurther distinction over instances where methyl silicone" is used toinclude the monomethyl compound, the term dimethyl silicone will be usedherein to designate the substantially dehydrated compound (CHahSiOhaving the polymeric unit structure Parrmrrou or Dnurm Smcour LIQUIDS 1.Pure dimethyl diethoxy silicane,

(CHJMSHOCaHDa is prepared in accordance with the method described andclaimed in our copending application Serial Number 416,285, fliedOctober 23, 1941 We have found that many desirable features rendering itsuitable for the above mentioned and other purposes are possessed by anorganosilicon oxide of the class known as silicones, more specificallydimethyl silicone. In the chemical literature the term "silicone refersto those silicon compounds in which two organic groups are combined withsilicon and oxygen according to the general formula R2810, B. being anorganic radical. In other words, the silicones are diorgano siliconoxides. The silicones in generalare polymeric and their unit structureis R *ii-O- The term silicone, as used herein, excludes the mono-organosilicon oxides in which only one (now Patent No. 2,380,057), whichcomprises. re-

acting nascent methyl magnesium Grignard with ethyl orthosilicate,SMOCaHsH, under pressure and fractionally distilling the product. Morespecifically, one moi equivalent of metallic magnesium is added to onemol equivalent of ethyl orthosilicate in a pressure tight vessel. Methylchloride gas is passed in until the ethyl orthosilicate is saturatedtherewith and a few cc. of ethyl bromide and a few crystals of iodineare then added to initiate the reaction, after which the reaction vesselis sealed and methyl chloride is again passed in until a total of onemoi equivalent thereof has been added. At the same time the reactionmixture is stirred and heat and pressure are developed. After some timethe temperature and pressure subside, indicating that the reaction hasceased, and the products of the reaction corresponding to the equation95% ethyl alcohol CHaCH-Sl OCaHs) 4+Mg- 1 (CH3) Si (OCaHs) 3+C2H5OMEC1CI-IaCl-l-CI-BS! (OCzHs) a +Mg- (CH3) 2S1 (OCzI-Is) 2+C2HsOMgCl arefractionally distilled. The boiling point of the dimethyl diethoxysillcane is 112 C. and the separation from the other components of themixture is relatively easy.

2. A pure dimethyl diethoxy silicane, preferably dissolved in ethylalcohol, is hydrolyzed with water. The hydrolysis may be conducted invarious ways and, although the resulting liquid will invariably have thesame chemical composition, its chemical structure and the physicalproperties dependent thereon can be varied substantially. In general,the use of a catalyst for promoting hydrolysis and the use of heatduring hydrolysis or during the subsequent drying of the product willincrease its viscosity.

Preferably, hydrolysis is carried out in the presence of an acidcatalyst by mixing one volume of the dimethyl diethoxy silicane with onevolume of a mixture of 95% ethyl alcohol and concentrated aqueoushydrochloric acid in equal parts. Although any acid may be used, weprefer to use acids which are easily removed by washing or which aredecomposed by heat, such as, hydrochloric, oxalic, acetic ortrichloracetic acids. Any concentration of acid may be used and for agiven acid the higher the concentration the higher the viscosity of theresulting liquid.

The temperature at which the hydrolysis is carried out will also aifectthe viscosity of the resulting liquid and the higher the temperature thehigher the viscosity or the more speedily does the liquid attain a givenviscosity. Hydrolysis may be effected at room temperature in abouteighteen hours but, preferably, the reaction mixture is refluxed forabout four to eight hours after which it ispoured into water and theproduct separates. The oily layer is washed free from acid and alcoholand is thereafter dried.

Drying may be accomplished without the use of heat by treating theliquid at room tempera ture with a drying agent such as anhydrous sodiumsulfate. When thus dried, the liquids which result from hydrolysis atroom temperature have a viscosity of about 100 Saybolt seconds at C.Liquids prepared without the use of a catalyst and without theapplication of heat will have still lower viscosities. If desired, theliquids may be dried and partially dehydrated by heating them at about120 C., or over, preferabiy'under reduced pressure whereby theviscosities. may range from 200 to 1000 or more Saybolt seconds at 25C., the viscosity increasing with.time and/or temperature of drying.Control of viscosity by heating will be hereinafter more fullydescribed.

3. A polymeric dimethyl silicone liquid was prepared as follows: Amixture consisting of the following:

' Per cent by volume Dimethyldiethoxysilane 50 Concentrated HCl 25 25was refluxed. The reflux was stopped at one hour and the product waswashed with water. Heating and stirring in a low pressure air streamserved to dry and at the same time to remove some low polymers from theliquid. The resulting liquid has a viscosity of -212 Saybolt seconds atC.,a flash 'point of 118 0., and an average-inopoint of 213 C; was heldat a temperature of 210 4 lecular weight of 1100. Column treatmentsserved to raise the flash point, the viscosity and the average molecularweight of the liquid as noted in table 1, given below. The columntreatment comprises flowing the liquid down the interior of anelectrically heated vertical column or tube packed with glass helicesagainst a counter-current of inert gas such as nitrogen, carbon dioxide,etc. Atmospheric or reduced pressure may be employed.

Table I Viscosity Column Avg. Mol. Temperaf g 2$}; Wt. Alter tureTreatment C. 6'. Liquid after drying" 212 1l8 I First Treatment 310 157l, 300 Second Treatment... 215 310 182 1, 300 Third Treatment.- 245 344244 l, 500

amounts of C02 bled in from dry ice in a Dewar flask. By exposing theliquid having the viscosity of approximately 212 Saybolt seconds to theabove column treatments for the proper length of time, i. e. of theorder of one minute, more or less, it is possible to prepare liquidshaving any desired viscosity between 212 and 344 Saybolt seconds and anydesired flash point between 118 C. and 244 C., and any desired molecularweight between 1100 and 1500.

Instead of the relatively brief column treatment described above, theliquid may be held at the desired temperature under reduced pressure andinert gas bubbled therethrough. This not only raises the flash point.but, if continued long enough, also causes a substantial increase inviscosity. In fact, the viscosity may be raised to any value above 344Saybolt seconds up to approximately 2000 Saybolt seconds by varying thetime of treatment. At the same time, the average molecular weight islikewise progressively increased. For example, a sample having aviscosity of 1190 Saybolt seconds (25 C.) and a flash 'C. and a pressureof 200 mm. while CO: was bubbled through it. After two hours theviscosity was 1660 Saybolt seconds flash point was 300 C. I

4. Dimethyldiethoxysilane was mixed with 34% by volume of 85% sulfuricacid. After being stirred for flve minutes, its viscosity was 720Saybolt seconds at 30 C. when washed free of acid. By continuing thetreatment with sulfuric acid for a sufllcient time, it is possibletoprepare a dimethyl silicone liquid having any desired viscosity up to15,000 Saybolt seconds at 30 C. and even higher. r

5. Liquid dimethyl silicone of about 900 Saybolt seconds viscosity wasprepared by. the hydrochloric acid-alcohol method of section 3 above.The liquid was placed in a thermostatically con.- trolled bath at 30 C.To this liquid was added 5.5% by weight of 98% sulfuric acid and themixture was stirred at 30 C. for four hours. The resulting product wasthen poured into about 5 to 10 volumes of water and stirred. It was thenallowed to stand for one hour with intermittent stirring, after which itwas taken up in benzene and washed three times with cold water, threetimes with dilute ammonia, three times with cold Water and three timeswith warm water. The

(25 C.) and the benzene solution wasthen placed in a distilling flaskand the benzene taken ofl on a water bath while a stream of carbondioxide was passed through. Following this, any low polymers wereremoved by raising the temperature to 230 C. while carbon dioxide waspassed through. The

viscosity of the product was 578,100 Saybolt seconds at 30 C. and itspour point was below 45 C.

By shortening the time of treatment with sulfuric acid, dimethylsilicone liquids of viscosities between 900 Saybolt seconds and 578,100Saybolt seconds were obtained. Or by continuing the treatment beyondfour hours, liquids up to and over 1,000,000 Saybolt seconds at 30 C.were ob- I tained. Liquids which exhibited little or no flow CHEMICALSTRUCTURE AND PROPERTIES The liquids prepared by the above describedprocesses are mixtures of dimethyl silicone polymers having the unitstructure hereinbefore referred to. They are soluble in organic solventssuch as benzene, toluene, etc. Analysis for carbon and silicon showedthat these polymers had a CHs/Si ratio of 2.0.

The above liquids ranging from liquids having approximately 200 Sayboltseconds viscosity at 30 C. to compositions having little or no flow atroom temperature have pour points less than -40 C., in many instances aslow as 65, and in some instances lower. They may also be heated above350 C. without decomposition. They may be heated at elevatedtemperatures for long periods without gelation. For example, they remainliquid and soluble when heated at 120 C. for four days or more in air.

The flash point of the liquids range between approximately 100 C. and ashigh as 350 0., depending upon their degree of polymerization and theamount of low molecular weight volatile polymers that are present. Formany purposes, particularly where high flash point was desired, it hasbeen found advisable to remove these low polymers by distillation up to150 C. at 4 mm. pressure. The resulting liquids not only have higherflash points and higher viscosities but also their viscosity-temperaturecoeflicients are greatly improved.

In general, the above described liquids exhibit relatively small changein viscosity as the temperature is varied as compared with petroleumoils. When petroleum oils are concerned, the relative changes ofviscosity with temperature are described numerically as a certainkinematic viscosity index (K. V. 1.). The equation for determining thisfigure is based on the known properties of standard petroleum oils at210 F. and 100 F. It is strictly valid only when giving an answerbetween 0 and 125. It takes no account of viscosities below 100 F. TheK. V. I. of the dimethyl silicone liquids of our invention liesgenerally in the neighborhood of 1'75 to 200, and their useful.properties are evident down to at least -40 C. We prefer to describe theviscositytemperature coefllcient or the change of viscosity 6 withtemperature as the slope of the line given by plottingv the logarithmsof the viscosity 1;, as ordinates against the reciprocals of theabsolute temperatures as abscissae. The lower the value of the slopebetween given temperatures, the smaller the change in viscosity of thematerial between these temperatures. The slope of a common petroleum oilGulf Pride 40" in terms of A log y Al/-T for the temperature interval to25 C. is 2218; for the temperature interval 25 to 50 C. is infinity. Theslopes of our new liquids similarly expressedfor the temperatureintervals 100 to 25 C. are in general less than about 1000 and in someinstances as low as approximately 600; for

the temperature interval 25 to 50 C., they are in general less than 2000and in many instances less than 1000.

Uses I These liquids are useful as lubricants and as hydraulic fluids.Their small change of viscosity with temperature means that smallchanges of energy sufllce to transmit pressure under different.

temperature conditions. The low pour point and high decomposition pointindicates that they are useful over a very wide temperature range. Theyare also useful as damping media for delicate instruments and for recoilmechanisms or shock absorbing devices not only on account of their lowtemperature-coeflicient of viscosity but because a wide range ofviscosities is obtainable. We have found that the liquids of ourinvention having viscosities between about 5000 and 250,000

Saybolt seconds at 30 C. and being substantially free of polymersdistillable up to 150 C. at 4 mm. are particularly useful for the aboveapplications.

Rubber does not swell, shrink nor become embrittled when in contact withliquid dimethyl silicone for extended periods of time, amounting to asmuch as a year or more. Consequently, these versatile liquids areadapted to be used in situations wherein common lubricating oils areentirely unsuitable, such as the lubrication of rubber bearings.

The wide range of temperatures over which they remain liquid makes ournew products useful as heat transfer media or as thermostat fluids. Theymay be used as circulating liquids for high or low temperaturemaintenance, or as the heat transfer media in high or low thermostaticbaths.

Measurement of the power factor of liquids prepared according to thisinvention showed this to be 0.05%. Consequently, such liquids can beused as the fluid filling medium for electrical power transformers.

We claim: I

1. A fluid composition composed of a mixture of liquid polymericdimethyl silicones having two methyl radicals attached to each siliconatom and a viscosity above 200 Saybolt seconds at 30 C.

2. A fluid composition composed of a mixture of liquid polymericdimethyl silicones having two methyl radicals attached to each siliconatom and a viscosity above 200 Saybolt seconds at 30 0., a flash pointabove C. and an average molecular weight above 1100.,

3. A fluid composition composed of a mixture of liquid polymericdimethyl silicones, having two methyl radicals attached to each siliconatom and having a viscosity between about 200 Saybolt seconds and 15,000Saybolt seconds at 30 C.

4- A fluid composition composed of a mixture I of liquid polymericdimethyl silicones having two methyl radicals attached to each siliconatom and a viscosity above 200 saybolt seconds at .30" 0., saidsilicones being substantially free of polymers distillableup to 150 C.at 4 mm. pressure.

5. A fluid composition composed of a mixture of liquid polymericdimethyl sillcones having two methyl radicals attached to I each siliconatom and a viscosity between about 5,000 and 250,000 Saybolt seconds at30 C.

6. A fluid composition composed of a mixture of liquid polymericdimethyl silicones having two methyl radicals attached to each siliconatom, a viscosity between about 200 and 350 S'aybolt seconds at 30. C.,a flash point between about-120 and 250 C., and an averagemolecularwelgh't between about 1100 and 1500, said silicones remainingliquid when heated at 120? C. for four days. I i v a 7. A lubricantcomprising a mixture of liquid polymeric dimethyl silicones having aviscosity greater than 200 Saybolt' seconds at 30 C. and aviscosity-temperature coeflfleient, as represented by the expressionwhere u is the viscosity and T the absolute temperature, not greaterthan 1000 for the temperature interval 100 to 25 C. and not 2000 for thetemperature interval 25 to -50 C.

greater than 30 2,258,218

8. A lubricant comprising a mixture of liquid polymeric dimethylsilicones having a viscosity between about 5000 and 250,000 Sayboltseconds at 30 0., said silicones being substantially free.

of polymers distillable up to.150 C. at 4 mm. pressure.

9. A lubricant composed of a. mixture of liquid dimethyl siliconeshaving the formula V 7 of liquid polymeric dimethyl silieones having anaverage molecular weight greater. than 740.

ROB ROY MCGREGOR. EARL LEATHEN WARRICK.

REFERENCES CITED The following references are of record in the file ofthis patent:

. UNITED STATES PATENTS Number Name Date 2,129,281 Lincoln Sept. 6, 1938Rochow Oct. 7, 1941 Rochow Mar. 6, 1945 I

